1. Field of the Invention
The present invention relates to optical line terminals and, more particularly, to an optical line terminal that detects and identifies a rogue ONT.
2. Description of the Related Art
A fiber-to-the-x (FTTx) passive optical network (PON) is a point-to-multipoint communications network. Examples of an FTTx network include a fiber-to-the curb (FFTC) network and a fiber-to-the-home (FTTH) network. In an FTT-x network, downstream data packets are transmitted from an optical line terminal (OLT) to a number of optical network terminals (ONT) that are located at or near a corresponding number of end users. Upstream data packets, on the other hand, are transmitted from the ONTs back to the OLT.
FIG. 1 shows a block diagram that illustrates a prior-art example of a point-to-multipoint communications network 100. As shown in FIG. 1, network 100 includes an OLT 110, a fiber optic cable 112, and a number of ONTs 114 that are connected to OLT 110 via fiber optic cable 112. Each ONT 114, in turn, is connected to an end user 116.
As further shown in FIG. 1, OLT 110 includes an interface unit 120 that is connected to cable 112, and an optical transmitter 122 that generates and outputs downstream data packets to the ONTs 114 via interface unit 120. In addition, OLT 110 includes an optical receiver 124 that receives upstream data packets from the ONTs 114 via interface unit 120.
OLT 110 also includes a MAC/processor 126 and a memory 128 that is connected to MAC/processor 126. MAC/processor 126 outputs downstream data to optical transmitter 122, and receives upstream data from optical receiver 124. Memory 128, in turn, stores the instructions and data required to operate MAC/processor 126.
In operation, OLT 110 establishes a sequence of transmission timeslots, and assigns transmission timeslots to the ONTs 114 that are connected to fiber optic cable 112. During normal operation, the ONTs 114 transmit data packets to OLT 110 during their assigned timeslots and only during their assigned timeslots.
One problem which can arise is when, due to a hardware or software failure, an ONT 114 transmits at the wrong time. If a first ONT transmits during a time slot which has been assigned to a second ONT and both ONTs attempt to transmit at the same time, a collision results which can prevent OLT 110 from being about to receive the data packets output by either ONT.
Thus, for example, when the optical transmitter of an ONT 114 “sticks on” and continuously transmits during all of the assigned time slots, the entire FTTx network can be rendered incapable of any communication between the ONTs 114 and OLT 110. An ONT that transmits in the upstream direction during the wrong time slot, such as a continuously transmitting ONT, is known as a “rogue ONT”.
Thus, in order to prevent a rogue ONT from incapacitating an entire a FTTx network segment, there exists a need for an OLT that can detect when an ONT has become a rogue and is illegally transmitting, and then identify which ONT is the rogue ONT so that service can be restored.